Bow sights range from simple pin markers to a vertically aligned series of pins mounted in a generally annular frame. Each pin corresponds to a particular distance to the target. The archer visually estimates the appropriate range and then sights to the target using the aiming pin corresponding to the estimated range.
Modern bow sights commonly use the illuminated end of an optical fiber as the sight point. The optical fiber absorbs ambient light through the side surfaces and projects the light out the end. The diameter of the optical fiber tended to be large in order for there to be enough surface area to gather sufficient light. The corresponding large size of the sighting end sometimes interferes with viewing of the target. Alternatively, a smaller diameter optical fiber can be used, but the length must be increased to add surface area to absorb light. It is preferred to wrap the excess optical fibers around a light transmitting structure to provide compactness.
The light conditions faced by hunters are highly variable in both intensity and color. If the sight is tuned for low light conditions, the amount of light projected by the optical fibers is too intense during high light conditions. Conversely, if the sight is tuned for high light conditions, not enough light will be absorbed and projected for low light conditions.
U.S. Pat. No. 7,290,345 discloses a pin sight that includes a light sensitive material, such as a photo chromic material, that regulates the amount of light absorbed by the optical fibers in proportion to the ambient light intensity in order to provide a more constant light intensity output.
Battery-powered lights used to selectively illuminate the pins solved the ambient light problem, but introduced the disadvantage of battery and light bulb failures. Battery-powered lights may also emit excessive light that may be seen by the quarry.
Even if these problems are overcome, the alignment of the shot can vary dramatically depending on where the archer positions his or her head, or more particularly, his or her shooting eye relative to the sight. If the archer's eye position varies from shot to shot, so will the accuracy and direction of each respective shot, leading to inconsistent or unpredictable shooting.
Peep sights are small devices which attach to the draw string on the bow and attempt to give the archer a consistent reference from which to position his or her eye. As noted in U.S. Pat. No. 5,850,700, there are numerous accuracy problems associated with mounting peep sights to a draw string, including, the draw string not being drawn the same exact distance each time and rotation of the draw string (and the peep sight) as it is drawn. The '700 patent proposes an eye alignment apparatus that assures that the archer's shooting eye is consistently positioned relative to the bow and the sight pins.